1. Field of the Invention
The instant invention relates to an apparatus for diffusing external light, such as that from a reflective TFT-LCD (Thin Film Transistor-Liquid crystal display), into a desired solid angle, which can be deviated from the unpleasant high intensity specular ray usually produced by the covering glass on the LCD.
2. Description of the Related Art
To facilitate later discussion, we first define the optics terms and variables that shall be used, as shown in FIG. 1. An incident plane is the plane containing the incident ray and the normal direction of the reflection point. A specular ray is defined as the reflected light ray on the incident plane whose reflected angle is equal to the incident angle. The light cone subtended by the diffused light is called a diffused light cone. Define the distribution angle of the diffused light cone in the incident plane as the vertical diffusion angle, xcex8S, and that perpendicular to the incident plane as the horizontal diffusion angle, xcex8T. A deviation angle xcex80 is the angle between the specular ray and the central ray in the diffused light cone.
Traditional reflective light diffusing elements, such as diffusive films (e.g., the Poloroid Holographic Reflector and Sumitomo Lumisty) or bump reflectors (e.g., U.S. Pat. No. 5,610,741 and R.O.C. Patent No. 255,019), cannot simultaneously achieve the goals of controlling the size of the diffused light cone, directing the reflected light distribution away from the specular ray, keeping the resolution power, and preventing color dispersion. However, for certain applications, the specular ray reflected by the covering glass is undesired because it is glare of the virtual image of the light source, and also, owing to the user""s viewing angle, one side of the usual diffused light cone around the specular ray will be useless. Since the efficiency of usual reflective TFT-LCDs is already as low as 10%, extra waste of diffused light will demand a stronger external light source and thus cause the reflective TFT-LCD to be even more unpractical than at present. Therefore, effectively controlling and smoothly distributing diffused reflected light within a specific solid angle to yield higher intensity and a more thorough use of reflected light from a reflective liquid crystal display (LCD) will be of great practical value.
One way to improve the above situation is by combining a diffusive film with a slant reflector structure. Although a diffused reflective light away from the specular ray can be achieved in this way, this method obviously increases the structure cost and, as a drawback of usual diffusive films, decreases the resolution of the LCD and causes the color dispersion problem.
Furthermore, an additional approach is to employ a mask being composed of areas having different transparencies to fabricate the slant reflector structure that is utilized in the LCD to avoid the resolution decrease and the color dispersion issue. Because the mask composed of areas having different transparencies is very expensive, the cost of the fabricated LCD is too much. So it is necessary to propose the other method without utilizing the mask composed of areas having different transparencies to fabricate the slant reflector structure employed by the LCD.
An object of the invention is to provide a diffusive-type light reflector which can reflect and diffuse incident light to a desired solid angle with required intensity uniformity and without degradation of display quality.
The invention provides a method for fabricating a diffusive-type light reflector which is a substrate having a plurality of bumpy elements with reflective curved surfaces. Each of the plurality of bumpy elements has a first surface and a second surface, the first angle (xcex1 or xcex8) between the first surface and the substrate being different from the second angle (xcex2 or xcfx86) between the second surface and the substrate.
A method for fabricating diffusive-type light reflector is proposed by the present invention. The diffusive-type light reflector is used for scattering incident light into a predetermined angular area away from specular ray. The method includes the following steps. First, a photoresist layer is formed on a substrate followed by exposure of the photoresist layer under defocus exposure through a slit-width-adjusting mask proposed by preferred embodiment of the present invention. The slit-width-adjusting mask includes a plurality sets of slits, each set of slits includes several portions, each portion is of the width p2. In addition, each portion includes a slit. The first portion under light source of the defocus exposure has a first exposure p1, and a second portion under light source of the defocus exposure has a second exposure q1. The transparent area within the second portion has width q2, the first exposure p1 is greater than the second exposure q1, and (q2)/(p2)=(q1)/(p1).
Then the photoresist layer is baked followed by development of the photoresist layer to form a photoresist pattern. The photoresist pattern includes a plurality of bumps, each of the plurality of bumps includes a first surface and a second surface, the first surface having a longer slant than that of the second surface. A first angle xcfx86 between the first surface and the substrate is unequal to a second angle xcex8 between the second surface and the substrate.
Subsequently, a reflective layer is formed on the photoresist pattern, with the normal direction of the first surface pointing to a predetermined direction enabling reflective light of the incident light reflected by the reflective layer to be scattered into the predetermined angular area.
As described above, according to the invention, each of the first surfaces has a monotonically convex and/or concave curve in the incident plane for scattering incident light into a desired angular area in the incident plane with specific intensity uniformity.
Further, as described above, according to the invention, each of the first surfaces has an irregular curve in the incident plane. Although the curve is irregular, the incident light will still be scattered into a certain angular area in the incident plane, yet the intensity uniformity is not guaranteed because of the irregular surface.
Yet further, according to the invention, each of the first surfaces has a wavy curve in the horizontal plane for scattering light into a desired solid angle with specific intensity uniformity.
Further according to the invention, each of the first surfaces has an irregular curve in the horizontal plane. Again, in spite of the irregularity, the incident light will be scattered into a certain solid angle without the guarantee of intensity uniformity.
Yet further, the invention provides a slit-width-adjusting mask for the photo-exposure procedures for making a diffusive-type light reflector according to the instant invention, wherein the mask comprises an opaque plate with a plurality of regular wavy slits with fixed separation or irregular wavy slits with fixed separation.